The goals are to immunochemically characterize the lymphocyte receptor for complexed antibody; to evaluate the genotypic and phenotypic expression of the receptor; and to evaluate the role of this receptor in the immune response. Further analysis of the Fc receptor of T lymphocytes for specificity and possible relationships with Ia antigens and other alloantigens will be undertaken. Study of the Fc receptor of macrophages for possible relationships with Ia antigens in order to assess possible similarities between the Fc receptors of different immunocompetent cell populations.